What
size and how many pieces should I hang?

First,
look at the size of the wall. Is it short, long or very tall? For
long wall, consider hanging six or seven 16 by 20s in a row with
minimal spacing, like three inches, between them. For shorter walls,
consider a montage effect with a couple large and smaller-sized
pieces stacked in an irregular fashion. For tall walls, consider a
few large pieces - somewhere in the neighborhood of 30 inches by 40
inches. Decorators can add dimension to their walls by adding
shelving to house art. Hang art from the wall, prop it on a shelf -
get creative!